Application method: impacts on atrazine and alachlor movement, weed control, and corn yield in three tillage systems

Banding herbicides reduces the agrochemical input compared to broadcast applications, and thereby reduces negative environmental impacts of herbicides. This study evaluated the impact of three tillage systems (ridge tillage, chisel plow, and moldboard plow) and two preemergence herbicide application methods (band and broadcast) on atrazine and alachlor movement, weed control, and corn (Zea mays L.) yield on two soils, one with a loam and the other with a silty clay loam texture in the surface layer. A 25 cm or 38 cm herbicide band applied over a 76 cm corn row compared to broadcast application reduced herbicide input by 67-50%, respectively. Shallow cultivation was used for weed control between rows in all tillage systems. Tillage system did not impact herbicide movement, weed control, or corn yield. Although less than 1% of the applied herbicide was detected in soil below 45 cm, atrazine and alachlor were found in water samples collected from pan lysimeters buried 90 cm below the surface. Banding reduced atrazine and alachlor collected in lysimeters by 50% and 80%, respectively, compared to a broadcast application for continuous corn; in finer textured soil. However, even in the banded application, atrazine levels in some years increased from <0.1 (background) to a maximum of 0.8 mu g l(-1) in a shallow aquifer 5.5 m below the surface of the silty clay loam soil when managed as a soybean [Glycine max (L.) Merr.] - corn rotation using the ridge tillage system. Yellow foxtail (Setaria glauca (L.) Beauv.) was the most abundant weed in the loam soil where corn yield was similar in band and broadcast treatments because cultivation could be and was timely after rainfall. In the silty clay loam soil, corn yields were less in banded than broadcast treatments in one out of the three years. Yield reductions in the banded treatment on this silty clay loam soil were attributed to poor control of Russian thistle (Salsola iberica Sennen and Pau), redroot pigweed (Amaranthus retroflexus L.), ladysthumb (Polygonum persicaria L.), and yellow foxtail because cultivation could not be done timely after rainfall. (C) 1998 Elsevier Science B.V. All rights reserved.